1. Field of the invention
The present invention relates to battery separators for placing between charged plates within a battery. More particularly, the present invention relates to such a battery separator which includes a non-woven fiber mat, in which one or more component fibers have a specific cross-sectional shape and exhibit a microcapillary action.
2. Description of the Relevant Art
Many types of electrical storage batteries are known and are widely used. Batteries, of the type which use internal charged metal plates, normally will also include porous non-conductive separators between the plates to insulate them from directly touching one another.
For example, a fairly standard prior art design for an electrical storage battery 110 is shown in FIG. 1. A prior art battery of this type is disclosed in U.S. Pat. No. 4,440,838. In this standardized design, which is widely used today, a hollow plastic casing 111 contains a plurality of positive plates 112, joined together by a conductive connector bar 114 which is attached to a positive terminal 116. The positive plates 112 alternate with a plurality of negative plates 118, and in similar fashion, the negative plates are joined together by a conductive connector bar 115 which is attached to a negative terminal 117. Each of the negative plates 118 is surrounded by a sleeve 120, made out of two sheets 122, 123, joined together at the outer edges thereof The sheets are formed of separator material.
It is known to make such battery separators out of nonwoven polymeric fibers. Examples of such battery separators may be found in U.S. Pat. Nos. 3,811,957, 3,875,270, 3,947537, 4,705,809, 5,158,844, and 5,318,866.
U.S. Pat. No. 4,137,379, issued in 1979 to Schmidt et al. and entitled xe2x80x9cStorage Battery with Separator of Dumbbell-Shaped Fibersxe2x80x9d discloses a storage battery in which a compressed mat of non-woven fibers is used as a fabric separator to space apart battery plates. The fibers making up the separator of Schmidt et al. have a dumbbell-shaped cross-sectional profile.
The assignee of the present invention has developed a new type of hollow fiber, having a longitudinally extending internal cavity therein, which may exhibit a xe2x80x98wickingxe2x80x99 or microcapillary action when placed into a fluid. Examples of these fibers, and some possible applications thereof, are given in U.S. Patent Nos. 5,069,970, 5,713,971, 5,759,394, 5,891,221 and 5,951,744.
While the known battery separators are useful for their intended purposes, a need still exists in the art for an improved battery separator which can promote fluid flow therethrough. It would also be advantageous if a battery separator were to be made of fibers having hollow channels formed therein to promote fluid flow therethrough.
The present invention has been developed to overcome the foregoing limitations and disadvantages of known battery separators, and to generally fulfill a need in the art for a battery separator adapted to promote the flow of fluids therethrough.
The present invention provides a battery separator for placement between conductive plates of a battery, including a non-woven fiber mat made up of a at least one, and preferably a plurality of nonwoven fibers. Each of the fibers includes an outer surface, a hollow internal cavity, and an extended slot. The hollow internal cavity communicates with the outer surface by way of the extended slot. The hollow internal cavity has a maximum width at an interior portion thereof, and the width of the slot is less than the maximum width of the internal cavity.
In a preferred embodiment, each of the nonwoven fibers includes a central stem and a plurality of substantially T-shaped lobes extending radially outwardly from the stem.
Optionally, the fiber mat may include a substantially continuous extended length hollow fiber, which is wrapped back on itself multiple times.
Capillary forces within the hollow fibers are greater than those on the fiber surface, such that a liquid electrolyte readily moves through the interior of the fiber via a xe2x80x98wickingxe2x80x99 action. As a result, the battery separator tends to direct fluid to adjacent battery plates, even when the battery electrolyte level drops below the tops of the plates.
Thermoplastics are a preferred material for the fibers. Preferably, the material making up the fibers is selected from the group consisting of polyolefins, fluoropolymers, polyimides, polysulfones, polyesters, polyamides, and mixtures thereof It is an object of the present invention to provide an improved battery separator which is usable in conjunction with a liquid electrolyte.
Another object of the present invention is to provide an improved battery separator which tends to direct liquid electrolyte to adjacent battery plates, even when an electrolyte level within the battery casing drops below the top of the plates.
For a more complete understanding of the present invention, the reader is referred to the following detailed description section, which should be read in conjunction with the accompanying drawings. Throughout the following detailed description and in the drawings, like numbers refer to like parts.